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    • G
      Bluetooth: Fix deadlock in the ERTM logic · e454c844
      Gustavo F. Padovan 提交于
      The Enhanced Retransmission Mode(ERTM) is a realiable mode of operation
      of the Bluetooth L2CAP layer. Think on it like a simplified version of
      TCP.
      The problem we were facing here was a deadlock. ERTM uses a backlog
      queue to queue incomimg packets while the user is helding the lock. At
      some moment the sk_sndbuf can be exceeded and we can't alloc new skbs
      then the code sleep with the lock to wait for memory, that stalls the
      ERTM connection once we can't read the acknowledgements packets in the
      backlog queue to free memory and make the allocation of outcoming skb
      successful.
      
      This patch actually affect all users of bt_skb_send_alloc(), i.e., all
      L2CAP modes and SCO.
      
      We are safe against socket states changes or channels deletion while the
      we are sleeping wait memory. Checking for the sk->sk_err and
      sk->sk_shutdown make the code safe, since any action that can leave the
      socket or the channel in a not usable state set one of the struct
      members at least. Then we can check both of them when getting the lock
      again and return with the proper error if something unexpected happens.
      Signed-off-by: NGustavo F. Padovan <padovan@profusion.mobi>
      Signed-off-by: NUlisses Furquim <ulisses@profusion.mobi>
      e454c844